This invention relates to sunglass lenses, both prescription and nonprescription, and more particularly relates to sunglass lenses having a laminated construction.
Sunglasses have been used for many years as cosmetic devices and to reduce the intensity of visible light. More recently they have come to be seen as important in protecting a wearer's eyes from harmful rays of the sun. In particular, exposure to light having ultraviolet (UV) rays can cause irreparable damage to the eye. Visible light ranges from about 380 to 700 nanometer. Opinions sometime differ as to the exact boundaries of this range. For example, some consider 400 nanometers to be the lower end of the range. We will consider 380 nanometers to be the lower end of the range in this specification. Wavelengths shorter than 380 nanometers fall below the visible light spectrum and represent the ultraviolet light spectrum. Wavelengths from 290 to 315 nanometers as known as UVB and can cause more damage than those in the range of 315 to 380 nanometers, known as UVA. Excessive exposure of the eyes to ultraviolet rays can damage the cornea and lens of the eye. Lifetime exposure to ultraviolet contributes to some types of cataracts. Additionally, the lens shields the light sensitive retina at the back of the eye from UV rays.
The lenses of higher quality sunglasses contain UV absorbers to protect the wearer's eyes from these damaging rays. UV absorbers are often included in the glass or plastic material used to make the lenses. They have also been included in lens coatings and, in the case of polarized lenses discussed in more detail below, in polarizing film laminated into the lens structure.
Sunglasses are familiar devices generally constructed from a frame and one or more lenses. The lenses may be glass or plastic. These lens materials may contain light absorbing dyes and ultraviolet inhibiting chemicals and may have one or more coatings applied to the lens after it is formed.
While most sunglass lenses have a unitary construction in that they are formed from a single piece of lens material, laminates have also been used as sunglass lenses. One type of laminate lens includes glass-plastic composite lenses. The idea of such lenses is to combine the light weight of a plastic lens with the superior surface and optical qualities of glass. Examples of such composite lenses are found in U.S. Pat. Nos. 4,227,950, 5,323,191, and 5,364,487. These composites are usually formed by bonding preformed glass and plastic elements with an adhesive (although U.S. Pat. No. 4,227,950 teaches casting the plastic lens element against a preformed glass lens element). Also see U.S. Pat. No. 5,351,100, which shows a glass multifocal ophthalmic lens formed by fusing a glass multifocal lens portion to the convex outer surface of a second lens portion.
A distinct class of sunglass lens laminates is those incorporating polarizing films. Light waves from the sun are random non-polarized waves which will reflect off a flat surface to become directional, or polarized. Glare is an example of light waves that have been restricted to one plane. Polarized sunglasses are effective at cutting surface reflection from flat surfaces such as water, ice, or roads. Polarizing lenses typically will have a polarizing layer laminated between two lens portions. Polarized sunglasses filter out glare, ultraviolet waves and other random light by use of a polarized light filtering film commonly made of polyvinyl alcohol dyed with iodine. This film is constructed so that its crystal molecules are aligned in parallel lines. Light waves perpendicular to the plane of the crystals are blocked and light waves in the same plane as the crystals pass through the membrane. See U.S. Pat. No. 5,135,298.
Some adhesives used in lamination of lens portions have low concentrations of UV absorbers. Addition of a UV absorber will keep the adhesive from yellowing upon exposure to UV light. The concentration of the absorber will be low. See U.S. Pat. No. 5,618,863.
There are many commercial examples of polarized lenses on the market. One type includes lenses that consist of two tempered clear glass lens portions. Another type includes lenses that consist of one front tempered clear glass and an untempered colored rear glass. This particular commercial lens may have a mirror surface on the external convex surface and an antireflective coating on the external concave surface. Color may be added to the polarizing film and may also be incorporated into the rear lens. Another type of commercial lens has a clear and untempered front glass with the rear glass lens being clear and tempered. The mirror is on internal front lens surface with the antireflective surface on external rear surface. Color is in the polarizing film only. The laminates containing the polarizing film are usually prepared using an adhesive curable with ultraviolet light.
The manufacture of currently available polarizing lenses is a complex, time-consuming procedure with inconsistent results. Multiple lens portions must be kept in inventory and a high quantity of lenses failing quality tests leads to high costs. Furthermore, the polarization efficiency of the lens laminates degrades unacceptably as a result of exposure to ultraviolet light during use.